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Active Ca 2+ transport systems in basolateral membranes from rabbit distal colon
Author(s) -
WIENER H.,
JONG M. D.,
OS C. H.
Publication year - 1990
Publication title -
journal of internal medicine
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.625
H-Index - 160
eISSN - 1365-2796
pISSN - 0954-6820
DOI - 10.1111/j.1365-2796.1990.tb01483.x
Subject(s) - ruthenium red , amiloride , biophysics , epithelial polarity , vesicle , membrane , ion transporter , calcium , membrane transport , apical membrane , chemistry , biochemistry , sodium , biology , organic chemistry
. Active Na + absorption by tight epithelia such as frog skin and distal colon share common features like feedback inhibition of cellular [Na + ] on Na + influx through amiloride‐sensitive Na + channels. It is postulated that the negative feedback of increasing cell [Na + ] is mediated via a rise in cell [Ca 2+ ]. In this model, cell [Na + ] is coupled to cell [Ca 2+ ] via a Na + /Ca 2+ exchange system in the basolateral membrane. In the present study, the Ca 2+ transporting systems in rabbit distal colon basolateral membranes were characterized. ATP‐dependent Ca 2+ uptake could be demonstrated in membrane vesicles from surface cells with the following kinetic parameters: K m = 0.09 μM Ca 2+ and V m = 3.8 nmol Ca 2+ mg −1 protein min −1 . The ATP‐dependent Ca 2+ transport was not responsive to ruthenium red and oxalate, suggesting a plasmalemmal origin. The addition of 75 mM Na + to the uptake medium, 10 min after addition of ATP, did not release Ca 2+ from the vesicles in significant amounts. In the absence of ATP, outwardly directed Na + gradients were incapable of stimulating Ca 2+ uptake. This study demonstrates that rabbit distal colon epithelium lacks a well‐defined Na + /Ca 2+ exchange system, and (Ca 2+ , Mg 2+ )‐ATPase appears to be the sole Ca 2+ extrusion system. Alternatives for the coupling of cell [Na + ] to cell [Ca 2+ ] are discussed.